Waheed Arshad
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PhD Title
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Dimorphic fruits, seeds and seedlings in Aethionema arabicum as adaptation mechanisms to abiotic stress in unpredictable environments |
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Research Theme
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Evolution and Adaptation |
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Primary Supervisor
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Abstract
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Diaspores – here, fruits and seeds – function as higher plant dispersal units, eminently adapted to a highly varied and changeable environment. While most plant species commit to a monomorphic propagation strategy, diaspores may exhibit heteromorphism, where two or more different types of fruits or seeds are produced by a single individual plant. One species exhibiting this intriguing phenomenon is Aethionema arabicum, an annual belonging to the earliest diverging lineage of the Brassicaceae family, which exhibits true diaspore dimorphism with no intermediate morphs. It has the remarkable ability to produce two morphologically distinct fruit (dehiscent and indehiscent) and seed (mucilaginous and non-mucilaginous) morphs on the same inflorescence. This thesis elucidates the eco-physiological, biomechanical, and molecular mechanisms of dimorphic fruits, seeds, and seedlings. A biophysical trait- based approach reveals contrasting syndromes associated with the promotion and prevention of diaspore dispersal. Together with fracturing biomechanics, these constitute important attributes leading to fruit dehiscence and abscission. Comparative imaging and transcriptome analyses during reproductive development provides an insight into the distinct mechanisms underpinning the transition from an unfertilised ovule to a dispersed seed propagule, namely in the development of seed coat mucilage. A large-scale screening of tissue-specific traits, under a range of abiotic stresses, reveals resilience of the derived seedlings and a time-course for transcriptional “resetting” during seed germination and early seedling growth. This results in plants developing from the two different seed morphs that are indistinguishable upon maturity. The independent PhD work builds on resources and knowledge from the ERA-CAPS SeedAdapt project, establishing how seed and fruit heteromorphism functions as a “bet-hedging” strategy in variable and unpredictable environments. The presented findings make Ae. arabicum an attractive model species for continuing and future research on diaspore dimorphism. |
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